1. Field of the Invention
This invention relates to a hose used for conveying a refrigerant containing an ester oil as a refrigerator oil (lubricant) to an electrically driven compressor. This invention is suitable for use with, among others, an electrically driven compressor in an automobile air conditioner.
2. Description of the Related Art
FIG. 1 shows by way of example a hose which has hitherto been used for transporting a refrigerant to an engine driven compressor in an automobile air conditioner. It comprises an inner tube 1 formed from e.g. IIR (isobutylene-isoprene rubber), a reinforcing layer 2 formed by e.g. braided fiber and an outer tube 3 formed from e.g. EPDM (ethylene-propylene-diene rubber). This structure has been employed to give the hose resistance to vibration, and resistance and impermeability to a refrigerant composed of a refrigerator oil containing PAG (polyalkylene glycol) and a flon substitute, such as HFC (hydrofluorocarbon).
A hybrid car driven by both a gasoline engine and an electric motor, and an "economical running" car having a gasoline engine adapted to stop instead of idling are being developed for practical use to avoid the global environmental problems caused by massive consumption of gasoline. In either event, the air conditioner which can be employed is of the type in which an electrically driven compressor is employed instead of an engine driven one which does not work if the engine is stopped.
An electrically driven compressor is required to have a high degree of electric insulation, since the motor is installed in a refrigerator. Accordingly, it is necessary to change the refrigerator oil containing PAG to an ester oil, e.g. POE (polyol ester), having a high degree of electric insulation. It is necessary to ensure a high degree of waterproofness against an external source in order to maintain the high electric insulation of the compressor and avoid the hydrolysis of the ester oil.
It has, however, been a drawback of the hose as shown in FIG. 1 that the IIR of the inner tube 1 is likely to swell with an ester oil easily and cannot be expected to be satisfactorily resistant or impermeable to any refrigerant for an electrically driven compressor. It has been another drawback thereof that the hose as a whole is not so designed as to be highly waterproof, but fails to resist any invasion of water through its wall from an external source satisfactorily.
Although no such problem may arise from a metal pipe used for transporting a refrigerant to an electrically driven compressor in an ordinary cabinet refrigerator, etc., it is impossible to use a metal pipe for transporting a refrigerant to a compressor in an automobile air conditioner, since a metal pipe is too rigid to withstand any vibration of the automobile, or its engine, particularly if the compressor is installed in the engine compartment.